A surface-protecting film is generally stuck to subject to be protected with pressure sensitive adhesive applied on the side of the protecting film, and used for the purpose of preventing scratches or staining caused during processing or conveyance of the subject to be protected. For example, a liquid crystal display panel is formed by sticking optical members such as a polarizing plate and a wavelength plate to a liquid crystal cell with pressure sensitive adhesive. The protecting film is stuck to these optical members stuck to the liquid crystal cell with pressure sensitive adhesive for the purpose of preventing scratches, staining and the like.
Then, the protecting film is removed by peeling off at the stage when the protecting film becomes unnecessary, for example, this optical member is stuck to the liquid crystal cell. Generally, the protecting film and the optical member are composed of plastic materials, so that electrical insulating property is high and static electricity is caused during friction and peeling off. Therefore, even when the protecting film is peeled off from the optical member such as polarizing plates, static electricity is generated. If the generated static electricity remains when a voltage is applied to the liquid crystal, the liquid crystal molecule can be out of alignment, or the panel can be damaged. Thus, in order to prevent such defects, various antistatic treatments are applied to the surface-protecting film.
For example, a method of preventing electrification by adding one kind or more of a surfactant to pressure sensitive adhesive to transfer the surfactant from the pressure sensitive adhesive to an adherend is disclosed (for example, refer to Patent Publication 1). However, with regard to this invention, the surfactant bleeds on the surface of the pressure sensitive adhesive so easily that staining on the adherend is concerned in the case of applying to the protecting film. Accordingly, when a pressure sensitive adhesive agent containing a low-molecular weight surfactant is used for optical member-protecting films, sufficient antistatic properties are difficult to provide without degradation of the optical properties of the optical member.
Also, a method of adding an antistatic agent comprising polyether polyol and an alkali metal salt to acrylic pressure sensitive adhesive to restrain the antistatic agent from bleeding on the surface of the pressure sensitive adhesive is disclosed (for example, refer to Patent Publication 2). However, bleeding of the antistatic agent can not be avoided also in this method; consequently, in the case of actually applying to the surface-protecting film, it has proved that treatment with time and under high temperature causes staining on the adherend due to the bleeding phenomenon.
Patent Publication 1: JP-A No. 9-165460
Patent Publication 2: JP-A No. 6-128539